The invention relates to a method for severing glass tubes or plates by thermal softening.
The severing of glass tubes and plates is one of the frequently occurring operations during the processing and treatment of glass tubes and plates. The most frequently used severing method consists of bursting or breaking, based on producing a tension zone in the glass and in some cases a weak point created by an initial scoring, after which the glass tube or plate can be severed with the formation of a fissure. These methods are extremely quick, but they have the disadvantage that the fissure does not always run precisely along the desired line of severance, and mainly that the breaking point has sharp edges and presents the danger of injury unless the edges are not eased by fusion. Furthermore, in the case of thin glass, heating may not create sufficient breaking tensions. In the case of mechanical breaking, possibly by means of preliminary scoring, unstable ends develop so that cracks running in the direction of the length of the tube may be created.
It is also known to sever glass tubes by thermal softening wherein the glass is softened at the severance point, and the softened parts are removed from one another by further heating, which is accomplished either automatically by the effect of gravity or by drawing them apart mechanically. A method of this kind is described, for example, in Russian Patent 9 66 048. A disadvantage of this method is that frequently a bead forms at the severance point and its diameter is greater than the wall thickness of the tube. Especially in the case of glass tubes with a wall thickness of 0.25 mm and less, severance by thermal softening has been impossible without the formation of a bead along the edge. The bead, however, is extremely undesirable in many applications, because the bead at the severance point gives the glass tube a different outside and inside diameter than the remainder of the tube.
It is likewise known to cut glass by means of a high intensity laser beam. In this case the glass is evaporated by the laser beam along the severance line. The disadvantages of this process are resulting high thermal tensions in the glass, the condensation of vaporized glass and its decomposition products in the vicinity of the severance point, and sometimes undesirable beading.
The present invention is addressed to the problem of providing a method for the heat-softened severance of thin glass plates and glass tubes, in which neither a greater outside diameter nor a smaller inside diameter than those of the original tube will result, and in which no bead will be formed that is greater than the thickness of the glass plate.
The various features of novelty which characterizes the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects obtained by its use, and reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.